Flexible multi-layer polyimide film laminates and preparation thereof

ABSTRACT

A process of making flexible multilayer polyimide metal-clad laminates, and their preparation, having at least one layer of aromatic polyimide bonded to at least one layer of a metallic substrate using a heat-sealable copolyimide adhesive containing repeating imide units derived from 4,4&#39;-oxydiphthalic dianhydride and an aromatic ether diamine. The laminates are used in flexible printed circuits and tape automated bonding applications. Additionally, the metallic substrate may be directly coated with the copolyimide adhesive and used as a single-clad laminate for flexible printed circuits.

This is a division of application Ser. No. 07/878,483, filed May 5,1992, now U.S. Pat. No. 5,298,331, which is a continuation-in-part ofapplication Ser. No. 07/571,913, filed Aug. 27, 1990, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to flexible multilayer polyimide metal-cladlaminates comprising at least one layer of an aromatic polyimide and atleast one layer of a metallic substrate for use in flexible printedcircuits and tape automated bonding applications. The invention alsorelates to a process for producing these laminates.

Laminates comprising one or more layers of polyimide and one or morelayers of metallic substrate material may be used for a variety ofapplications. For example, polyimide coated metal foils, due to theflexibility and outstanding mechanical, thermal and electricalproperties of polyimides, can be used for printed electrical circuits.This is because the laminates are frequently exposed to hightemperatures during further processing, for example, during soldering ordrilling. The laminates also have to satisfy stringent requirements inregard to their electrical and mechanical properties.

Laminates comprising only one substrate layer of metal or metal alloyand a layer of polyimide, so called single clads, may be used forprinted electrical circuits. The same applies to multilayer laminates,so called multi-clads or multilayer circuits, which comprise severalmetal layers and/or several polyimide layers.

Laminates containing polyimides and metal substrates are well-known inthe art. Usually the polyimide layers are bonded to the metal substrateby a conventional adhesive. For example, U.S. Pat. No. 3,900,662 andU.S. Pat. No. 3,822,175 disclose bonding of polyimide to metal using anacrylate-based adhesive. However, it has been found that whenconventional adhesives such as acrylates, epoxides, polyamides, phenolicresins etc. are used to bond the polyimide to the metal, the resultinglaminates do not exhibit entirely satisfactory properties which meet thestringent demands often imposed. Conventional adhesives do not generallypossess the high temperature heat stability of the polyimide materialitself, and the strength of the adhesive bonds in multilayer laminarpolyimide structures deteriorates rapidly when subjected to elevatedtemperatures.

On account of the disadvantages of laminates comprising layers ofconventional adhesives between polyimide and metal, multilayer laminateshave been proposed in which the polyimide is bonded directly to metal,i.e. without a layer of adhesive. Thus, British Patent 2,101,526discloses the bonding of a polyimide derived frombiphenyltetracarboxylic dianhydride directly to metal foil by applyingheat and pressure. In other words, the polyimide is formable. It hasbeen found, however, that such formable polyimides have inferior thermalstability to conventional non-formable polyimides.

The object of this invention is to provide flexible polyimide metal-cladlaminates, which withstand high temperatures, have good adhesion, goodthermal, mechanical and electrical properties and are chemicallyetchable (for TAB applications).

SUMMARY OF THE INVENTION

According to the present invention there is provided a flexiblepolyimide metal-clad suitable for use in a flexible printed circuit andtape automated bonding comprising at least one layer of a metallicsubstrate and at least one layer of an aromatic polyimide, said layer ofpolyimide being bonded on at least one side to said layer of metallicsubstrate with a peel strength of at least 4 pli through an adhesivelayer of a heat-sealable copolyimide comprising at least 60 mole % ofrepeating imide units of the formula ##STR1## and not greater than 40mole % of other repeating imide units of the formula ##STR2## wherein Ris an aromatic tetravalent organic radical and R' is a divalent radicalof an aromatic or aliphatic diamine containing at least two carbonatoms, the two amino groups of said diamine each being attached to aseparate carbon atom of said divalent radical.

A further embodiment of the invention relates to a polyimide laminatecomprising a layer of a metallic substrate coated on one or both sideswith the aforesaid copolyimide adhesive suitable for use as asingle-clad laminate for flexible printed circuits.

A still further embodiment of the invention relates to a process forpreparing an adherable all-polyimide laminate for use in makingmetal-clads comprising coating a copolyamic acid adhesive directlyeither on a fully cured polyimide base film, or on a partially curedpolyimide gel or green film or by coextruding the copolyamic acid withthe polyimide base film and then curing to form the copolyimide.

DETAILED DESCRIPTION OF THE INVENTION

The polyimide film metal-clad laminates of the present inventioncomprise at least one layer of a polyimide base film which on at leastone of its two sides is bonded to a metal using a heat-sealablecopolyimide adhesive as specifically defined hereinafter. Alternatively,the copolyimide adhesive may be directly bonded to one or both sides ofthe metal substrate.

The polyimide base films used in the laminates of the invention arepreferably about 0.3 to 5 mils in thickness and can be obtained frompolyamic acid precursors derived from the reaction of suitable diamineswith suitable dianhydrides in the manner described in, for example, U.S.Pat. No. 3,179,614.

Dianhydrides which can be used in the polyimide base film include:

pyromellitic dianhydride;

3,4,9,10-perylene tetracarboxylic dianhydride;

naphthalene-2,3,6,7-tetracarboxylic dianhydride;

naphthalene-1,4,5,8-tetracarboxylic dianhydride;

bis(3,4-dicarboxyphenyl) ether dianhydride;

bis(3,4-dicarboxyphenyl) sulfone dianhydride;

2,3,2',3'-benzophenonetetracarboxylic dianhydride;

bis(3,4-dicarboxyphenyl) sulfide dianhydride;

bis(3,4-dicarboxyphenyl) methane dianhydride;

2,2-bis(3,4-dicarboxyphenyl) propane dianhydride;

2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane;

3,4,3',4'-biphenyltetracarboxylic dianhydride;

2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;

2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;

2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;

phenanthrene-1,8,9,10-tetracarboxylic dianhydride;

pyrazine-2,3,5,6-tetracarboxylic dianhydride;

benzene-1,2,3,4-tetracarboxylic dianhydride; and

thiophene-2,3,4,5-tetracarboxylic dianhydride.

Diamines which can be used together with the dianhydrides in thepolyimide base film include the following:

meta-phenylenediamine;

para-phenylenediamine;

2,2-bis(4-aminophenyl) propane;

4,4'-diaminodiphenylmethane;

4,4'-diaminodiphenyl sulfide;

4,4'-diaminodiphenyl sulfone;

3,3'-diaminodiphenyl sulfone;

4,4'-diaminodiphenyl ether;

2,6-diaminopyridine;

bis(3-aminophenyl) diethyl silane; benzidine;

3,3'-dichlorobenzidine;

3,3'-dimethoxybenzidine;

4,4'-diaminobenzophenone;

N,N-bis(4-aminophenyl)-n-butylamine;

N,N-bis(4-aminophenyl) methylamine;

1,5-diaminonaphthalene;

3,3'-dimethyl-4,4'-diaminobiphenyl;

m-aminobenzoyl-p-aminoanilide;

4-aminophenyl-3-aminobenzoate;

N,N-bis(4-aminophenyl) aniline;

2,4-bis(beta-amino-t-butyl) toluene;

bis(p-beta-amino-t-butylphenyl) ether;

p-bis-2-(2-methyl-4-aminopentyl) benzene;

p-bis(1,1-dimethyl-5-aminopentyl) benzene;

m-xylylenediamine;

p-xylylenediamine;

position isomers of the above, and mixtures thereof.

The preparation of polyimides and polyamic acids is more fully describedin U.S. Pat. No. 3,179,614 and U.S. Pat. No. 3,179,634.

A particularly preferred polyimide base film is derived from4,4'-diaminodiphenyl ether and pyromellitic dianhydride.

The heat-sealable copolyimide adhesives used in the present inventionmay be either random or block and contain at least 60 mole % ofrepeating imide units of the formula ##STR3## and not greater than 40mole % of other repeating imide units of the formula ##STR4## wherein Ris an aromatic tetravalent organic radical and R' is a divalent radicalof an aromatic or aliphatic diamine containing at least two carbonatoms, the two amino groups of the diamine each being attached toseparate carbon atoms of the divalent radical.

The heat-sealable copolyimide adhesive contains at least 60 mole %,preferably from 40 to 80 mole % and, most preferably, from 70 to 80 mole% of imide units derived from 4,4'-oxydiphthalic dianhydride (ODPA) andan aromatic ether diamine of the formula ##STR5## If the percentage ofsuch imide units is lower than 60 mole %, it is difficult to obtaincopolyimide adhesives having glass transition temperatures less than250° C. and good adhesion on the substrates.

Representative aromatic ether diamines include:

1,2-bis(4-aminophenoxy) benzene

1,3-bis(4-aminophenoxy) benzene

1,2-bis(3-aminophenoxy) benzene

1,3-bis(3-aminophenoxy) benzene

1-(4-aminophenoxy)-3-(3-aminophenoxy) benzene

1,4-bis(4-aminophenoxy) benzene

1,4-bis(3-aminophenoxy) benzene

1-(4-aminophenoxy)-4-(3-aminophenoxy) benzene

The addition of up to 40 mole %, preferably from 2 to 25 mole %, andmost preferably from 5 to 15 mole % of additional imide units of theformula ##STR6## wherein R and R' are as previously defined above, tothe copolyimide adhesive provides the requisite low glass transitiontemperature (<250° C.) and thermal stability of adhesion properties (>4pli) without reducing the good thermal, mechanical and electricalproperties characteristic of the polyimide.

Such additional imide units may be derived from dianhydrides anddiamines which are the same or different from the 4,4'-oxydiphthalicdianhydride and aromatic ether diamines previously defined.

Particularly preferred dianhydrides and diamines include the following:

pyromellitic dianhydride;

4,4'-oxydiphthalic dianhydride;

3,3',4,4'-benzophenone tetracarboxylic dianhydride;

2,2',3,3'-benzophenone tetracarboxylic dianhydride;

3,3',4,4'-biphenyl tetracarboxylic dianhydride;

2,2',3,3'-biphenyl tetracarboxylic dianhydride;

2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride;

bis(3,4-dicarboxyphenyl) sulfone dianhydride;

bis(3,4-dicarboxyphenyl) sulfide dianhydride;

bis(2,3-dicarboxyphenyl) methane dianhydride;

bis(3,4-dicarboxyphenyl) methane dianhydride;

1,1-bis(2,3-dicarboxyphenyl) ethane dianhydride;

1,1-bis(2,3-dicarboxyphenyl) propane dianhydride;

2,2-bis(3,4-dicarboxyphenyl) propane dianhydride;

m-phenylene bis(trimellitate)dianhydride;

hexamethylene diamine;

heptamethylenediamine;

3,3'-dimethylpentamethylenediamine;

3-methylhexamethylenediamine;

3-methylheptamethylenediamine;

2,5-dimethylhexamethylenediamine;

octamethylenediamine;

nonamethylenediamine;

1,1,6,6-tetramethylhexamethylenediamine;

2,2,5,5-tetramethylhexamethylenediamine;

4,4-dimethylheptamethylenediamine;

decamethylenediamine;

meta-phenylenediamine;

4,4'-diaminobenzophenone;

4-aminophenyl-3-aminobenzoate;

m-aminobenzoyl-p-aminoanilide;

4,4'-diaminodiphenylether;

3,4'-diaminodiphenylether;

bis(4-aminophenyl) methane;

1,1-bis(4-aminophenyl) ethane;

2,2-bis(4-aminophenyl) propane;

4,4'-diaminodiphenyl sulfoxide;

3,3'-diaminobenzophenone;

1,3-bis(4-aminophenoxy) benzene;

2,2'-diaminobenzophenone;

1,2-bis(4-aminophenoxy) borone;

1,3-bis(4-aminobenzoyloxy) benzene;

4,4'-diaminobenzanilide;

4,4'-bis(4-aminophenoxy) phenyl ether;

2,2'-bis(4-aminophenyl) hexafluoropropane;

2,2-bis(4-aminophenyl) -1,3-dichloro-1,1,3,3-tetrafluoropropane;

4,4'-diaminodiphenyl sulfone;

1,12-diaminododecane;

1,13-diaminotridecane;

polysiloxane diamine of the formula ##STR7## wherein R₄ is loweralkylene, aralkylene or phenylene, R₅ is lower alkyl or phenyl, R₆ islower alkyl or phenyl and m is 1 to 100. The term "lower" includes from1 to 3 carbon atoms.

Particularly preferred copolyimide adhesives of the invention containfrom 70 to 95 mole % of oxydiphthalic dianhydride, 5 to 30 mole % ofpyromellitic dianhydride and 100 mole % of1,3-bis(4-aminophenoxy)benzene and from 80 to 95 mole % oft,3-bis(4-aminophenoxy)benzene, 5 to 20 mole % of hexamethylene diamineand 100 mole % of oxydiphthalic dianhydride.

The copolyimide adhesives of the present invention exhibit excellentphysical properties including an elastic modulus of under 400 kpsi toprovide the necessary conformability, a low coefficient of thermalexpansion (<100 ppm), dielectric constant (<3.5), dielectric strength(2.5-3.5 volts/mil), dissipation factor (0.001-0.01), water absorption(<2.5%) and solder resistance.

Chemical etchability of the copolyimide adhesive can be obtained bychemically converting the precursor polyamic acid using conversionchemicals such as acetic anhydride and beta-picoline. The chemicallyconverted copolyimide adhesive, when coated on chemically convertedpolyimide base film, provides a chemically etchable film laminate whichcan be used in TAB applications. Chemical etchability can also beachieved by incorporating ester functionality in the adhesive backboneusing a diester diamine (RDEDA) or a diester dianhydride (MPBTDA) ascomonomer.

Ideally the adhesives are cured at temperatures ranging from 150° C. to400° C. by raising the temperature in increments of 5° C./min to 300° C.over 90 minutes and heating at 400° C. for 5 minutes and then laminatedat 350° C. to obtain high bond strengths. Higher cure temperatures tendto reduce the bondability of the adhesive. Longer residence times athigh temperatures also reduce the bond strength.

For example, the adhesive ODPA/PMDA:RODA (80/20:100) when coated onpolyimide green film and cured at 150°-300° C. and laminated to copperfoil at 350° C. for 20 min and 150 psi pressure gave a peel strength of12 pli. When the same film is cured at 400° C. for an additional 5minutes and laminated at 350° C. the peel strength dropped to 10 pli.Longer than 10 minutes curing at 400° C. may cause reduced bondstrengths. The polyimide laminates of the present invention can beprepared by applying a thin coating of a copolyamic acid precursor ofthe desired copolyimide described above to the polyimide base film ordirectly to a metallic substrate and thereafter treating the coatedpolyimide base film or coated metallic substrate to completely convertthe polyamic acid precursor to polyimide. Coating thicknesses range from0.1 to 2 mil. The base polyimide film will of course be different fromthe coating polyimide.

The copolyamic acid precursors are prepared by reacting approximatelyequimolar amounts of the aforesaid dianhydrides and diamines in an inertorganic solvent such as N,N-dimethylacetamide or N-methylpyrrolidone.Other organic solvents such as N,N-dimethylformamide, dimethylsulfoxide, xylene, toluene and tetrahydrofuran can also be used ascosolvents.

The polyamic acids can be converted to polyimides by either a thermalconversion process or a chemical conversion process using a dehydratingagent and a catalyst to give distinct products having different adhesivecharacteristics.

Copolyimide adhesive coatings can be applied to fully cured polyimidebase film or to one of the intermediate manufacturing stages such as to"gel" film or to "green" film.

The term "gel" film refers to a sheet polyimide material which is ladenwith volatiles, primarily solvent, to such an extent that the polyimideis in a gel-swollen, plasticized, rubbery condition. The volatilecontent is usually in the range of 80 to 90% by weight and the polymercontent usually in the range of 10 to 20% by weight of the gel film. Thefilm becomes self-supporting in the gel film stage and can be strippedfrom the support on which it was cast and heated. The gel film generallyhas an amic acid to imide ratio between 90:10 and 10:90.

The gel film structure can be prepared by the method described in U.S.Pat. No. 3,410,826 by mixing a chemical converting agent and a catalyst,such as a lower fatty acid anhydride and a tertiary amine, respectively,into the polyamic-acid solution at a low temperature, followed bycasting the polyamic-acid solution in filmform, on a casting drum andmildly heating the cast film at, for example, 100° C. to activate theconversion agent and catalyst for transforming the cast film to apolyamic acid-polyimide gel film.

Another type of polyimide base film which can be coated with thecopolyimide adhesive is "green film" which is all polyamic acid or whichhas a very low polyimide content. Green film contains generally about 50to 75% by weight polymer and 25 to 50% by weight solvent and issufficiently strong to be self-supporting.

Green film can be prepared by casting the polyamic acid solution intofilm form onto a suitable support such as a casting drum or belt andremoving the solvent by mild heating at up to 150° C. A low proportionof amic acid units in the polymer, e.g., up to 25%, may be converted toimide units.

Application of the copolyamic acid coating can be accomplished in anynumber of ways, such as by slit die, dipping or kiss-roll coating,followed by metering with doctor knife, doctor rolls, squeeze rolls orair knife. It ,may also be applied by brushing or spraying.

Using such techniques, it is possible to prepare both one- and two-sidecoated structures. In preparation of the two-side coated structures, onecan apply the coatings to the two sides either simultaneously orconsecutively before going to the curing and drying stage.

In another embodiment, the polyamic acid adhesive solution can becoextruded onto one or both sides of the polyamic acid gel base or greenfilm and the polyamic acid layer(s) subsequently cured by heattreatment.

In a further embodiment, the polyamic acid adhesive may be coated on afully cured polyimide base film or directly on a metal substrate andsubsequently imidized by heat treatment. The polyimide base film may beprepared by either a chemical or thermal conversion process and may besurface treated, e.g. by chemical etching, corona treatment, laseretching etc., to improve adhesion.

A single polyimide metal-clad of the present invention comprises aflexible copolyimide layer which adheres to a metal foil such as copper,aluminum, nickel, steel or an alloy containing one or more of thesemetals as a substantial constituent, or to a foil of amorphous metal.The copolyimide layer adheres firmly to the metal and has a high peelstrength of 4 pli and higher. The metals do not have to be used aselements in pure form, i.e. it is also possible to use substrates ofmetal alloys, such as alloys containing nickel, chromium or iron ornickel and copper, or of amorphous alloys containing iron. Particularlysuitable metallic substrates are foils of rolled, annealed orelectrodeposited copper or rolled, annealed copper alloy. In many cases,it has proved to be of advantage to pretreat the metallic substratebefore coating. The pretreatment may consist of a chemical treatment ora mechanical roughening treatment. It has been found that thispretreatment enables the adhesion of the copolyimide layer and, hence,the peel strength to be further increased. Apart from roughening thesurface, the chemical pretreatment may also lead to the formation ofmetal oxide groups, enabling the adhesion of the metal to thecopolyimide layer to be further increased. It has been found thatapproximately a 0.2 pli increase in peel strength results for eachmicroinch increase of surface roughness.

A polyimide multi-clad of the present invention comprising a double sidecopper clad can be prepared by laminating copper foil to both sides ofan adhesive coated dielectric polyimide film. The construction can alsobe made by laminating adhesive coated copper foil to both sides of adielectric polyimide film or to an adhesive coated dielectric polyimidefilm.

The advantageous properties of this invention can be observed byreference to the following examples which illustrate, but do not limit,the invention. All parts and percentages are by weight unless otherwiseindicated. ##STR8##

EXAMPLES 1-30

Polyamic acid solutions were prepared by reacting the appropriate molarequivalents of the monomers in dimethylacetamide (DMAC) solvent.Typically, the diamine(s) (0.05 mole) dissolved in DMAC were stirredunder nitrogen and the dianhydride(s) (0.05 mole) were added as solidover a period of several minutes. Stirring was continued to obtainmaximum viscosity of the copolymer. The viscosity was adjusted bycontrolling the amount of dianhydride in the polyamic acid composition.

The copolyamic acids were coated on a fully cured corona treatedpolyimide base film derived from pyromellitic dianhydride and4,4'-diaminodiphenyl ether and converted to copolyimide either by athermal conversion process or by a chemical conversion process usingacetic anhydride as dehydrating agent and betapicoline as a catalyst toprovide distinct products having different adhesive characteristics.

The copolyamic acids were coated on the base polyimide film using acoating bar to a thickness of 0.5 mils and the solvent removed byheating at 80° C. for 20 minutes. The coated polyimide films were placedon a pin frame and Examples 1 to 19 were cured at 160° to 220° C. andExamples 20 to 30 were cured at 160° to 260° C. for 90 minutes.

The coated polyimide films were subsequently laminated to roll-annealedcopper at temperatures of 250° C., 300° C. and 350° C. to form thecopper-clads.

Roll clads could also be made by continuous lamination of the adhesivecoated dielectric film to copper foil using a high temperature doublebelt press or a high temperature nip roll laminator.

Peel strength results of the polyimide copper-clad laminates weredetermined by ASTM method IPC-TM-650, Method No. 2.4.9B and are given inTables I and II.

                                      TABLE 1                                     __________________________________________________________________________    Peel Strength of Chemically Converted Adhesive on Corona                      Treated 2 mil PMDA/ODA Polyimide Film                                         Example                                                                            Adhesive Compo-  Peel Strength (pli)                                     No.  sition (mole %)  250° C.                                                                    300° C.                                                                    350° C.                                                                    Tg (°C.)                             __________________________________________________________________________    Control                                                                            ODPA:RODA                                                                     100:100          1.0 4.4 4.8 215                                              ODPA:RODA/SiODA                                                           1   100:95/5.sup.a       2.9 4.6 202                                          2   100:90/10.sup.a      1.3 3.2 190                                              ODPA/PMDA:RODA                                                            3   70/30:100.sup.a      3.9 4.5 220                                          4   80/20:100.sup.b  2.2 8.4 6.4.sup.c                                                                         225                                          5   90/10:100.sup.a      3.9 5.5.sup.c                                                                         222                                              ODPA-RODA/HMD                                                             6   100:90/10.sup.a      4.8 5.4.sup.c                                                                         209                                          7   100:80/20.sup.a      3.8 4.3 201                                              ODPA/6FDA:RODA                                                            8   90/10:100.sup.a  4.9 4.0 4.5 221                                          9   80/20:100.sup.a  4.3 5.2.sup.c                                                                         7.6.sup.c                                                                         227                                         10   70/30:100.sup.a  4.1 4.9     232                                              ODPA/PMDA-RODA/HMD                                                       11   90/10:90/10.sup.a                                                                              4.2 4.4 4.8.sup.c                                                                         210                                         12   80/20:80/20.sup.a                                                                              3.6 5.3 4.9 204                                              ODPA/6FDA/PMDA:RODA                                                      13   70/15/15:100.sup.b                                                                             1.44                                                                              3.8 3.6 230                                         14   60/20/20:100.sup.b                                                                             1.5 3.3 4.3 235                                         15   80/20:95/5.sup.a 3.5 4.7     215                                         16   80/20:90/10.sup.b                                                                              4.2 3.0     213                                         17   80/20:97.5/2.5.sup.b                                                                           4.9 4.8     212                                              ODPA/PMDA/MPBTDA:RODA                                                    18   70/20/10:100         5.2 5.4                                                  ODPA/PMDA:RODA/RDEDA                                                     19   80/20:90/10          5.6 4.6                                             __________________________________________________________________________     .sup.a Bond failure between polyimide and adhesive                            .sup.b Bond failure between copper and adhesive                               .sup.c Maximum bond strength before the base film tears.                 

                                      TABLE II                                    __________________________________________________________________________    PEEL STRENGTH OF THERMALLY CONVERTED                                          ADHESIVE ON CORONA TREATED                                                    2 mil PMDA/ODA POLYIMIDE FILM                                                 Example                                                                            Adhesive Compo-     Peel Strength (pli)                                  No.  sition (mole %)     250° C.                                                                    300° C.                                                                    350° C.                                                                    Tg (°C.)                          __________________________________________________________________________         ODPA/PMDA:RODA                                                           20   20:100              7.7  6.5.sup.c                                                                        6.3.sup.c                                                                         225                                           ODPA/PMDA:RODA/SiODA                                                     21   20:95/5.sup.b       9.0 10.0    215                                      22   20:90/10.sup.a      7.5  9.5.sup.c                                                                            213                                      23   20:97.5/2.5.sup.b   4.9  6.sup.c                                                                              212                                           ODPA:RODA/HMD                                                            24   0:90/10.sup.a            7.sup.c                                                                              209                                           ODPA/6FDA:RODA                                                           25   20:100.sup.a        5.0  5.1                                                                              5.2 227                                           ODPA/PMDA:RODA/HMD                                                       26   20:80/208                6.sup.c                                                                              204                                           ODPA/BTDA:RODA                                                           27   20:100                   5.6                                                                              Film Breaks                                       ODPA/PMDA:RODA/DABA                                                      28   20:80/20                 9.0                                                                              7.2 236                                           ODPA/BTDA:RODA/SiODA                                                     29   20:95/5                  4.6                                                                              5.5 209                                           ODPA/PMDA:RODA/DABA/SiODA                                                30   20:75/20/5               3.5                                                                              8.0 215                                      __________________________________________________________________________     .sup.a Bond failure between Polyimide and Adhesive                            .sup. b Bond failure between Copper and Adhesive                              .sup.c Maximum bond strength before the base film tears                  

EXAMPLES 31-55

Polyamic acid solutions were prepared as described in Examples 1 to 30and coated on a polyamic acid "green film" derived from reaction ofpyromellitic dianhydride and 4,4'-diaminodiphenyl ether. The coatedpolyimide film was heated at 80° C. for 20 minutes to remove most of thesolvent, placed on a pin frame and dried and cured at 160°-260° C. for90 minutes followed by 5 minutes at 400° C.

Copper-clad polyimide laminates were prepared as previously describedand peel strengths were determined. Results are given in Table III.

EXAMPLE 56

A copolyamic acid containing 80 mole % ODPA, 20 mole % PMDA and 100 mole% RODA was prepared as previously described and coated and cured on a"green" film, a "gel" film and a fully cured polyimide film derived fromreaction of PMDA and ODA. Properties of the ODPA/PMDA/RODA adhesive aregiven in Table IV.

Polyimide copper-clad laminates were prepared using both roll-anneal-ed(RA), electrodeposited (ED) and brass-treated (JTC) copper foils. Peelstrength results are given in Table V.

                                      TARLE III                                   __________________________________________________________________________    Peel Strength of Thermally Converted Adhesive                                 on PMDA/ODA Polyimide "Green" Film                                            Example                                                                            Adhesive Compo-  Peel Strength (pli)                                     No.  sition (mole %)  250° C.                                                                    300° C.                                                                    350° C.                                                                    Tg (°C.)                             __________________________________________________________________________         ODPA:RODA                                                                Control                                                                            100:100                   9.0                                                                              215                                              ODPA:RODA/SiODA                                                          31   100:95/5                  4.5                                                                              202                                         32   100:90/10                 6.0                                                                              190                                              ODPA/PMDA:RODA                                                           33   70/30:100                 9.5                                                                              220                                         34   80/20:100                11  225                                         35   90/10:100                10.5                                                                              222                                              ODPA:RODA/HMD                                                            36   100:90/10                10.5                                                                              209                                         37   100:80/20                Film                                                                              201                                                                       Breaks                                               ODPA/6FDA:RODA                                                           38   90/10:100                 9  221                                         39   80/20:100                 8.5                                                                              227                                         40   70/30:100                 9  232                                              ODPA/PMDA:RODA/SiODA                                                     41   80/20:95/15               4.5                                                                              215                                         42   80/20:90/10               4.0                                                                              213                                         43   80/20:97.5/2.5            4.5                                                                              212                                              ODPA/BPTA:RODA                                                           44   80/20:100             9.0                                                                              10.0                                                                              224                                              ODPA/BTDA:RODA                                                           45   80/20:100             8.0                                                                               8.5                                                                              224                                              ODPA:RODA/PPD                                                            46   100:80/20             8.0                                                                               9.5                                                                              228                                              ODPA:RODA/ODA                                                            47   100:80/20             7.0                                                                               7.5                                                                              227                                              ODPA/PMDA:RODA/ODA                                                       48   80/20:80/20           5.0                                                                              10.sup.c                                                                          235                                              ODPA/DSDA:RODA                                                           49   80/20:100             7.sup.c                                                                           8.5                                                                              225                                              ODPA/PMDA:RODA/BAPE                                                      50   80/20:70/30               7.7                                                                              228                                              ODPA/PMDA:RODA/MPD                                                       51   80/20:70/30               6.6                                                                              247                                              ODPA/PMDA/MPBTDA:RODA                                                    52   70/20/10:100          7.5                                                                               9.0                                                 ODPA/PMDA:RODA/RDEDA                                                     53   80/20:90/10           7.5                                                                               9.6                                                 ODPA/PMDA:RODA/RDEDA                                                     54   80/20:95/5           10.0                                                     ODPA/PMDA:CODA                                                           55   80/20:100             8.2                                                                              10.2                                            __________________________________________________________________________     .sup.c Maximum bond strength before the base film tears.                 

                  TABLE IV                                                        ______________________________________                                        PROPERTIES OF ADHESIVE ODPA/PMDA/RODA FILM                                    ______________________________________                                        Tensile Strength:       11 kpsi                                               Elongation:             23%                                                   Modulus:                345                                                   Shrinkage at 200° C.:                                                                          0.2%                                                  Glass Transition Temperature:                                                                         220° C.                                        Dielectric Constant:    3.38                                                  Dielectric Strength:    2.96 volts/mil                                        Dissipation Factor:     0.0016                                                Coefficient of Thermal Expansion (CTE):                                                               60 PPM                                                Water Absorption:       0.93%                                                 Density:                1.362                                                 Tear Strength:          5.8 gm/mil                                            Moisture Content:       0.163%                                                ______________________________________                                    

                                      TABLE V                                     __________________________________________________________________________    PEEL STRENGTH OF ODPA/PMDA:RODA                                               ADHESIVE ON VARIOUS COPPER FOILS                                                                         PEEL STRENGTHS (pli)                               ADHESIVE    COATED ON AND CURED                                                                          RA RA-JTC                                                                             ED ED-JTC                                  __________________________________________________________________________    ODPA/PMDA:RODA                                                                            "GREEN" FILM   11 7.5  24 12.5                                    (80/20:100)                                                                               "GEL" FILM     9.5                                                                              11.5 22 20                                                  FULLY CURED FILM                                                                             8       *                                          __________________________________________________________________________     *Base film broke; could not determine peel strength.                     

EXAMPLES 57-61

Various copper foils were used to make polyimide laminates with anODPA/PMDA:RODA (80/20:100) adhesive as shown in Table VI.

The results show that the arithmetic average roughness (AA) of the foilinfluences the measured peel strength. Over the range of roughnesstested, the ODPA/PMDA:RODA adhesive showed a 0.2 lb/in increase in peelstrength for each microinch increase in AA. The oxide and brasstreatments both produced a similar increase in peel strength over thatmeasured with an untreated surface.

                  TABLE VI                                                        ______________________________________                                        EFFECT OF COPPER SURFACE TREATMENT ON                                         PEEL STRENGTH OF ODPA/PMDA:RODA (80/20/100)                                   ADHESIVE                                                                                     AA       Peel Strength (pli)                                   Ex.  Copper    (Micro-  ODPA/PMDA:RODA(80/20:100)                             No.  Foil      inches)  Green Film                                                                            Gel Film                                                                             Cured Film                             ______________________________________                                        57   RA/oxide  6.7      4.5     --     --                                          (Brightside)                                                             58   RA/oxide  6.6      11      9.5    8.0                                    59   RA/brass  10.8     7.5     11.5   --                                     60   ED/brass  51.3     12.5    20     --                                     61   ED/oxide  72.6     24.0    22     --                                     ______________________________________                                    

EXAMPLES 62-65

Polyamic acid solutions were prepared as described in Examples 1 to 30and coated on a polyamic acid "gel film" prepared by chemical conversionof pyromellitic dianhydride and 4,4'-diaminodiphenyl ether. The coatedgel film was heated at 80° C. for 20 minutes to remove the solvent,placed on a pin frame and dried at 160°-260° C. for 90 minutes.

Copper-clad laminates were prepared as previously described and peelstrengths were determined. Results are given in Table VII.

                  TABLE VII                                                       ______________________________________                                        PEEL STRENGTH OF ADHESIVES ON                                                 PMDA/ODA GEL FTLM                                                                      Adhesive                                                                      composition      Peel Strength* (pli)                                Example  (mole %)         300° C.                                                                        350° C.                              ______________________________________                                        62       ODPA.RODA/HMD    8.0     6.5                                                  100:80/20                                                            63       ODPA:BPDA:RODA   5.5                                                          80/20:100                                                            64       ODPA:RODA/PPD    4.5     8.0                                                  100:80/20                                                            65       ODPA/PMDA:CODA   6.0     7.0                                                  80/20:100                                                            ______________________________________                                         *Bond failure between copper and adhesive.                               

What is claimed is:
 1. A process for preparing a polyimide laminatecomprising coating at least one side of a base film selected from thegroup consisting of polyamic acid green film, polyimide gel film andcured polyimide film with a solution of a copolyamic acid precursor of acopolyimide in an inert organic solvent and subsequently treating thecopolyamic acid coated base film to completely convert the copolyamicacid precursor to the copolyimide, wherein the copolyimide comprises atleast 60 mold % of repeating imide units of the formula ##STR9## and notgreater than 40 mole % of other repeating imide units of the formula##STR10## wherein R is the radical of a tetravalent organic carboxylicdianhydride selected from the group consisting of pyromelliticdianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylicdianhydride, 3,3','4,4'-biphenyl tetracarboxylic dianhydride,2,2',3,3'-biphenyl tetracarboxylic dianhydride,2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride and m-phenylenebis(trimellitate)dianhydride; and wherein R' is the radical of adivalent aromatic or aliphatic diamine selected from the groupconsisting of p-phenylene diamine, hexamethylene diamine, heptamethylenediamine, octamethylene diamine, 4,4'-diaminodiphenyl ether,3,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene,1,2-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminobenzoyloxy)benzene,4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)phenyl ether and apolysiloxane diamine, provided that said repeating imide units offormula (I) are different from said repeating imide units of formula(II).
 2. The process of claim 1 wherein the copolyamic acid precursor isthermally converted to copolyimide by heat treating at 160° to 260° C.for 90 minutes.
 3. The process of claim 1 Wherein the copolyamic acidprecursor is chemically converted to copolyimide by mixing a chemicalconverting agent and a catalyst with the copolyamic acid at atemperature of 80° C. and then heat treating at 160° to 220° C. for 90minutes.
 4. The process of claim 3 wherein the chemical converting agentis a lower fatty acid anhydride and the catalyst is a tertiary amine. 5.The process of claim 1 wherein the polyimide base film is a completelycured polyimide comprising pyromellitic dianhydride and4,4'-diaminodiphenyl ether.
 6. The process of claim 1 Wherein thepolyimide base film is a partially converted polyimide gel filmcomprising pyromellitic dianhydride and 4,4'-diaminodiphenyl ethercontaining from 20 to 80% reaction solvent.
 7. The process of claim 1wherein the polyimide base film is a substantially unconverted polyamicacid green film comprising pyromellitic dianhydride and4,4'-diaminodiphenyl ether containing from 20 to 80% polyamic acidpolymer from 20 to 40% reaction solvent.
 8. The process of claim 5wherein the copolyamic acid precursor comprises from 70 to 95 mole %oxydiphthalic dianhydride, 5 to 30 mole % pyromellitic dianhydride and100 mole % 1,3-bis(4-aminophenoxy) benzene.
 9. The process of claim 6wherein the copolyamic acid precursor comprises from 70 to 95 mole %oxydiphthalic dianhydride, 5 to 30 mole % pyromellitic dianhydride and100 mole % 1,3-bis(4-aminophenoxy) benzene.
 10. The process of claim 7wherein the copolyamic acid precursor comprises from 70 to 95 mole %oxydiphthalic dianhydride, 5 to 30 mole % pyromellitic dianhydride and100 mole % 1,3-bis(4-aminophenoxy) benzene.